RIO DE JANEIRO, Brazil (CNN) -- The Brazilian air force said that debris picked up Thursday near where officials believe Air France Flight 447 crashed Monday into the Atlantic Ocean was not from the plane.

Image released by the Brazilian Air Force shows oil slicks in the water near a debris site.

"It has been verified that the material did not belong to the plane," Brigadier Ramon Borges Cardoso told reporters in Recife about the material recovered Thursday. "It is a pallet of wood that is utilized for transport. It is used in planes, but on this flight to Paris, there was no wooden pallet."

He added that oil slicks seen on the ocean were not from the plane, either, and that the quantity of oil exceeded the amount the plane would have carried.

"No material from the airplane was picked up," he said.

The announcement left open the question of whether other debris that had not yet been plucked from the ocean might be from the plane.

On Wednesday, searchers recovered two debris fields and had identified the wreckage, including an airplane seat and an orange float as coming from Flight 447. Officials now say that none of the debris recovered is from the missing plane.

Helicopters had been lifting pieces from the water and dropping them on three naval vessels.

Brazilian Air Force planes spotted an oil slick and four debris fields Wednesday but rain and rough seas had kept searchers from plucking any of the debris from the water.

Officials said searchers had found objects in a circular 5-kilometer (3-mile) area, including one object with a diameter of 7 meters (23 feet) and 10 other objects, some of which were metallic, Brazilian Air Force spokesman Jorge Amaral said.

The debris was found about 650 kilometers (400 miles) northeast of the Fernando de Noronha Islands, an archipelago 355 kilometers off the northeast coast of Brazil.

Eleven aircraft and five ships are engaged in the search, including airplanes from France and the United States.

Earlier Thursday, a public interfaith service was held for the 228 victims at a 200-year-old Catholic Church in downtown Rio. Joining family members were members of the Brazilian armed forces, who are leading the recovery effort.

"Whoever has faith, whoever believes in God, believes in the eternity of the soul," said Mauro Chavez, whose friend lost a daughter on the flight. "This means everything."

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Investigators have not yet determined what caused the plane to crash. The flight data recorders have not been recovered, and the plane's crew did not send any messages indicating problems before the plane disappeared.

A Spanish pilot said he saw an "intense flash" in the area where Flight 447 came down off the coast of Brazil, while a Brazilian minister appeared to rule out a midair explosion.

Meanwhile, a report in France suggested the pilots were perhaps flying at the "wrong speed" for the violent thunderstorm they flew into early on Monday before the Airbus A330's systems failed.

Le Monde newspaper reported that Airbus was sending a warning to operators of A330 jets with new advice on flying in storms.

As several ships trawled the debris site in the Atlantic, Brazil's defense minister said a 20-kilometer (12-mile) oil slick near where the plane, en route from Rio de Janeiro to Paris, went down indicated it probably did not break up until it hit the water.

If true, that would rule out an in-flight explosion as the cause of the crash of Air France Flight 447, Defense Minister Nelson Jobim told reporters.

However, both pilots of an Air Comet flight from Lima, Peru, to Lisbon, Portugal, sent a written report on the bright flash they said they saw to Air France, Airbus and the Spanish civil aviation authority, the airline told CNN.

"Suddenly, we saw in the distance a strong and intense flash of white light, which followed a descending and vertical trajectory and which broke up in six seconds," the captain wrote.

Air Comet declined to identify the pilot's name but said he waited until landing to inform Air Comet management about what he saw. Air Comet then informed Spanish civil aviation authorities. The Air Comet co-pilot and a passenger aboard the same flight also saw the light.

But Robert Francis, former vice chairman of the U.S. National Transportation Safety Board, said the question of determining where a plane broke up "is a very difficult one to deal with." He told CNN's "Anderson Cooper 360" that "there are lots of things that cause a plane to go out of control."

He added that extremely strong winds are not unusual near Brazil. Pilots who fly over that part of the world keep track of radar and "are very, very wary about the weather as they go back and forth down in that area."

According to the officials, who had been briefed on the incident and declined to be identified because of the ongoing investigation, the Air France office in Buenos Aires received the threat from a man speaking Spanish.

Authorities checked the Boeing 777 and found nothing. Security was tightened during check-in for Flight 415, which left on time and without incident, the officials said.

Most of the people on Flight 447 came from Brazil, France and Germany. The remaining victims were from 29 other countries, including three passengers from the United States.